How to use DC voltage map of BFLEX25 main board
KLD BFLEX25 Bass amp is based on Ampeg PF20T, which power amp is Class AB amp of two 6L6 tubes. Below is introduction of the DC voltage map of main board of BFLEX 25, which could help hobbyists to understand tube amp working principles and troubleshooting after assembly. Please pay attention: The inner of tube guitar amp has fatal high voltage. If you have not enough skill and experience in high voltage circuit, do not try to test it by self. Measure condition of voltage map |
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DC voltage map of BFLEX25 main board |
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The second 12ax7 is Long Tail Pair(LTP) phase inverter of BFLEX25 amp.The grids (Pin2,7) of V2 connected with SKY and V2-8 of the board, the voltages of these two holes are 0VDC. The plates( Pin1,6) of V2 connected with V3-1 and V3-6 of the board.The voltage of V3-1 is 211VDC and V3-6 is 190VDC. The cathodes of V2 are Pin 3 and 8 of tube, they connected with one hole of the board V3-3/8, the voltage is 1.6VDC. |
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The power tube of BFLEX25 can use 6L6 or EL34 etc. The data in the voltage map were measured by 6L6. Pin2 and 7 are pins of filament. Pin3 is Anode(Plate) . The Pin 4 is grid2(Screen). Pin5 is grid1.Pin8 is cathode and beam plate. The type of power amp stage of BFLEX25 is Class AB : V3 and V4. The pins of these two 6L6 connect with the main board include: Pin2s(Filament)of V3 and V4 connect with board 6.3VAC; Pin4s(grid 2) of V3 and V4 connect with V4-9,V5-9 of the board, the voltages are 330VDC all; Pin5s(grid 1) connect with V5-2 and V4-2 of the board, one is -43VDC, one is -40VDC; Pin8s (Cathode) connected with V4/5-3 and R24C of the board, all are 80 mVDC. The static operating points is important parameters describing status of amp, it is useful tool to troubleshoot. Abnormal operating points always means not only connection in mistake, but also resoanace in circuit. |